Common Tin Electrical Connector Failure Mechanisms
When looking at the cause behind a majority of wearable electronic failures, often the first problem that occurs is a loss of contact between two conductors. Conductor failure is directly related to poor connector performance, and there are several reasons connectors fail. For starters, connectors are frequently overlooked as critical components in wearable design, due to the fact that they are not as sophisticated as the integrated circuits and complex technologies used to package them. Likewise, most wearables have thousands of opportunities for contact failure — any of which could shut the system down. For example, a wearable product can have connectors used in antennas, sensors, power/grounding, battery connections, board-to-board connection, flexible printed circuit connection, wire-to-board connection and removable memory cards.
An initial lack of communication and understanding between product designers and connector manufacturers can also lead to electrical connector failure in wearable devices. Because there are dozens of companies producing electrical connectors, subtle product quality differences can occur, which can impact reliability. A connector’s contact force, the hardness of the metal finish, the oxide layer, adsorbed gasses, and any physical contaminants are all dependent on production, and can impact the asperities, or contact points, of a reliable connection. These variances require connector engineers to have a firm grasp of contact physics in order to help ensure that predicted reliability is achieved.
The composition of tin itself can also pose reliability risks. It’s important to remember that tin is a soft metal that can grow a hard and brittle oxide. At a microscopic level, it is comparable to ice on mud. Once contact is made, the oxide is easily broken and fresh tin oozes through. Then, once contact is broken, the exposed tin re-oxidizes and must be broken through again. If new contact locations are frequently made due to displacement, the tin oxide can build up and eventually create a debris field that can prevent adequate contact from being made. This process is called fretting, and typically occurs on tin-plated connectors that are used in a vibrating environment, or in an application with many insertion/withdrawal cycles. Fretting can also occur with frequent temperature cycling that can lead to micromotion of the contacts.